1. Field of the Invention
The present invention relates to a bobbin for use in a motor, such as a stepping motor.
2. Description of the Related Art
The stepping motor is extensively used in office automation equipments and automotive applications. The stepping motor rotates stepwise at a fixed angle for each step in response to electrical signals generated by a digital control, thereby performing positioning function. A PM (permanent magnet) stepping motor, which has its rotor comprising a permanent magnet, is one type of stepping motor.
The PM stepping motor is manufactured, for example, such that components constituting a stator, such as stator yokes, a coil composed of a bobbin and a magnet wire wound around the bobbin, and the like, are set in place inside a molding die and integrally molded with resin, as disclosed in the Unexamined Japanese Patent Application KOKAI Publication No. Sho 63-274355. In the manufacturing method disclosed therein, the central axis of a rotor can be aligned to the central axis of the stator with a high degree of accuracy, thereby enhancing the motor performance characteristics. Thus, the manufacturing method mentioned above features the process of resin-molding for integration of components, which enables the components to be simultaneously set in predetermined position.
In the abovementioned manufacturing method, since molten resin is filled in at high pressure during the molding process, the magnet wire wound around the bobbin is likely to suffer deformation thereby causing insulation material of the magnet wire to deteriorate, and consequently triggering a layer short-circuit. And, even before the molding process, the magnet wire can be damaged due to mishandling of the coil.
The same applies not only to stepping motors but also to other type motors that include coils, thus posing a problem that magnet wires provided on bobbins are not satisfactorily protected, and therefore failing to ensure the reliability.